Fermentation is a step in the beer brewing process, which starts when yeast is added to wort in a container. During fermentation, sugars are metabolised into alcohol and carbon dioxide. As the sugar is metabolised, fermentation gradually slows down until the “end of fermentation”, when the beer is ready for further treatment such as conditioning, filtering or bottling. For home brewers, beer is bottled directly after fermentation has ended, for secondary fermentation and storage.
Fermentation typically takes between 4 and 7 days to complete, but this can vary depending on many factors, such as the temperature at which the fermenting wort is kept, the type of brew or the amount of yeast. However, it is important to accurately determine when fermentation has ended. As carbon dioxide gas is produced during fermentation, if the beer is bottled too early, this can result in a build up of pressure and eventually bottles may explode. On the other hand, if left to ferment for too long, the brew may spoil.
End of fermentation is currently determined when the specific gravity (SG) becomes stable over 24 hours (or reaches final gravity (FG)). The brewer will check for FG once it appears that carbon dioxide production has ceased. However, this method does raise some difficulties, because it requires efficient sealing at the measurement point, and the measurements can vary with temperature. Therefore, this method of measuring end of fermentation is not particularly suitable for automation. Furthermore, it generally requires contact with the wort, which is undesirable and can result in contamination if not performed correctly.
Accordingly, there is a need for alternative methods of testing for end of fermentation.